(a) Field of the Invention
The present invention concerns a semiconductor integrated circuit containing, on a common semiconductor substrate, at least one vertical static induction transistor and at least one vertical static induction type transistor wherein the former transistor is used to form a logic circuit region and the latter transistor, a peripheral circuit region such as an interface circuit, respectively, of a semiconductor integrated circuit to provide functions different from each other.
(b) Description of the Prior Art
Semiconductor integrated circuits are being used in various electronic devices and apparatuses. As is well known, these circuits are being advanced toward higher packing density and larger scale. Above all, the size and scale of electronic computers have, of late, been on the increase. Along with this, development is making rapid progress in the fabrication of such integrated circuits (IC), large scale integrated circuits (LSI) and very large scale integrated circuits (V-LSI) that are superior in high-speed operation and large capacity of their constituent logic circuits, controlling circuits and/or memory circuits. In the past, bipolar transistors have been well known in their employment in semiconductor integrated circuits for the purpose of providing high-speed operation. It has been difficult, however, in such known semiconductor integrated circuits, to design the logic circuit requirements of high-speed operation so as to be compatible with those requirements of the peripheral regions which are connected to the high-speed operation regions. For example, a digitalized LSI which is employed in, for example, an electronic computer is comprised of a circuit region such as a logic circuit region and a memory circuit region both of which require high-speed operation (such a circuit region will hereunder be referred to simply as a hardware region) and a peripheral circuit region including a so-called interface circuit region intended to operatively and functionally connect the hardware region to a desired device or devices. In case, for example, two bipolar transistors are used to form the two types of circuit regions mentioned above to constitute a semiconductor integrated circuit, the respective operating characteristics of these two bipolar transistors have been noted to conflict between the high-speed operation requirements and the good interface requirements. Therefore, in the designing of a semiconductor integrated circuit with bipolar transistors, aspects of either one of the two requirements has had to be sacrificed. More particularly, in order to satisfy the high-speed characteristic of the semiconductor integrated circuit exhibited by one of the constituent bipolar transistors, this specific bipolar transistor is required to have a narrow base width, since the frequency characteristic of a bipolar transistor depends mainly on the width of the base region thereof. Although a bipolar transistor having a narrow base width satisfies the high-speed operation of the hardware region, the peripheral region which is manufactured at the same time with the hardware region on the same principal surface of a semiconductor substrate will develop the so-called punch-through phenomenon due to the narrow base width of the bipolar transistor of the an interface circuit. Thus, the breakdown voltage is lowered, and the bipolar transistor constituting the hardware region will become broken. The breakdown voltage of the hardware region may well be low, since the operating voltage applied is usually low. Since, however, the operation voltage used for the peripheral circuit region is high, there is required a high breakdown voltage for that particular bipolar transistor constituting the peripheral circuit region.
For the reasons stated above, it will be noted that, in case a semiconductor integrated circuit is fabricated on a common semiconductor substrate by integrating the hardware circuit region and peripheral circuit region, there is the necessity to design so that the peripheral region has a breakdown voltage higher than the operating voltage, as a result of which the high-speed characteristic of the hardware region will, not be satisfied sufficiently. In such semiconductor devices as, for example, STL (Schottky Transistor Logic), ISL (Integrated Schottky Logic) and IIL (Integrated Injection Logic) which are all known typical semiconductor integrated circuits serving as logic circuits, there is ordinarily used a power supply having a voltage of about 1-2 V for operating the logic circuit of the hardware region. In contrast thereto, the power supply for the interface circuit in the peripheral circuit region is set to have a voltage of about 5 V to operate such interface circuits. Accordingly, in order to design so that the peripheral region has a breakdown voltage of about 5 V, the bipolar transistor which serves as an interface circuit region requires to have a breakdown voltage of 6-7 V. Accordingly, the high-speed operation of the other bipolar transistor provided in the logic circuit region which is formed at the same time with the interface bipolar transistor can no longer be expected to exert a sufficiently speedy operation.
In order to resolve this problem of semiconductor integrated circuits encountered in the past, there may be considered the fabrication of said hardware circuit region and said peripheral circuit region in separate steps relative to each other. Such manner of manufacture of a semiconductor integrated circuit, however, contributes only to complication of the process, leading to a reduction in the production yield and an increase in the manufacturing cost. This is especially so in the case of manufacture of bipolar transistors. A bipolar transistor is formed by relying on the planar technique. That is, its base width is determined by two selective diffusion steps which are called "base diffusion" and "emitter diffusion". Thus, the complication of the overall fabricating process will become all the more prominent.